Garden Talk: October 12, 2006

From NGA Editors

Research Links Acid Rain to Sugar Maple Decline

Colorful fall foliage is one of the characteristic signs of autumn throughout much of the eastern United States, and sugar maples, with their brilliant orange and red leaf colors, are one of the signature trees. Acid rain is threatening to reduce the number of sugar maples in our forests, alter the forest ecosystem, impact the maple sugar industry, and reduce the colorful fall brilliance. Although pollution controls since the 1960s have reduced the amount of sulfuric acid in the atmosphere, the amount of nitric acid from automobile pollution has not decreased. This has resulted in highly acidic forest soils.

Researchers at Cornell University investigated the influence of acid soils on sugar maple growth. Because nitric acid and sulfuric acid leach calcium -- an essential plant nutrient -- from the soil, in 1999 the researchers added calcium to a sugar maple test plot at their research facility in North Woodstock, New Hampshire, to replicate the soil conditions that existed 25 years ago, prior to the acid rain era. Every year since then, sugar maple growth in the test plot and in a similar, non-treated plot has been evaluated.

Within a few years the acidity in the top levels of the soil on the calcium-treated plot had neutralized. The sugar maples' response was better seed production, seedling germination, and root growth. Adult sugar maples in the untreated plot continued to decline and produced fewer seedlings.

This research suggests that highly acidic soils resulting from nitric acid pollution are creating a soil environment that's harmful to sugar maple growth and reproduction.

Gold Medal Dogwood

Since 1978 the Pennsylvania Horticultural Society (PHS) has annually recognized outstanding trees, shrubs, and woody vines. These plants are awarded the PHS Gold Medal for their eye appeal, performance, and hardiness in USDA zones 5 to 7. For 2007, PHS has added three new plants to their Gold Medal list.

The most outstanding of the new award-winners is the 'Venus' dogwood (Cornus Venus). Flowering dogwoods are beloved, small, spring-flowering trees that grow in the eastern United States. Unfortunately, they struggle in many yards due to diseases such as anthracnose and powdery mildew. Venus, however, is resistant to both diseases. It grows 25 feet high and wide at maturity and produces 6-inch-diameter pure white blooms in spring. This fast-growing tree can be grown in USDA zones 4 to 7.

New Technique for Protecting Blackberries

Trailing blackberry varieties such as Siskiyou and Chester Thornless are popular for their large-sized fruits and heavy production. But little commercial production of trailing blackberries takes place in areas colder than USDA zone 6 because of their lack of winter hardiness. A new technique developed at the Agricultural Research Service in Kearneysville, West Virginia, may help expand the growing range of these fruits.

Blackberries are normally grown on trellises to keep the canes erect. Researchers created a rotating, cross-arm trellis system that allows growers to bend the canes to the ground in winter. Then the canes can be covered with insulation, such as a floating row cover or plastic sheeting.

Trials on protected and non-protected canes of Siskiyou blackberries revealed that protected canes produced 3 to 5 times more fruit than non-protected canes and produced three weeks earlier. This technique may allow gardeners in areas colder than USDA zone 6 to consistently produce a good crop of trailing blackberries.

Warmer, Wetter Winter?

Trying to predict the severity of the upcoming winter in October is like trying to predict the winner of the Super Bowl in November. But over the years atmospheric researchers have found that one phenomenon seems to consistently impact global weather. El Nino.

El Nino is the cyclical warming of the waters in the tropical Pacific Ocean that affect temperature and rainfall around the globe. This fall El Nino has started to develop and may strengthen through the winter. If El Nino continues, predictions for winter weather in the United States include warmer-than-average temperatures across the west, the southwest, the plains states, the Midwest, most of the northeast, the northern mid-Atlantic, as well as most of Alaska. Wetter-than-average conditions are expected across the southwest from southern California to Texas, and for Florida and the southern Atlantic coast. Drier-than-average conditions are expected in the Tennessee valley, the northern Rockies, the Pacific Northwest, and Hawaii.